With the advance of weight-, thickness- and length-reducing technology in the field of the electronic and electric industry and with the recent advancement of weight-reducing technology in the fields of the automobile, aircraft and space industries, there has been a strong demand for crystalline thermoplastic resins having heat resistance of about 300.degree. C. or higher and permitting easy melt processing in recent years.
As crystalline, heat-resistant, thermoplastic resins developed to date, there are, for example, poly(butylene terephthalate), polyacetal, poly(p-phenylene thioether), etc. These resins are however unable to meet the recent requirement level for heat resistance.
Polyether ether ketone (hereinafter abbreviated as "PEEK") and polyether ketone (hereinafter abbreviated as "PEK") have recently been developed as heat-resistant resins having a melting point of about 300.degree. C. or higher. These resins are crystalline thermoplastic resins. It has therefore been known that conventional melt processing techniques such as extrusion, injection molding and melt spinning can be applied to easily form them into various molded or formed articles such as extruded products, injection-molded products, fibers and films. These resins however use expensive fluorine-substituted aromatic compounds such as 4,4'-difluorobenzophenone as their raw materials. Limitations are thus said to exist to the reduction of their costs. It is also pointed out that these resins involve a problem in expanding their consumption.
Based on an assumption that PTK could be promising candidate for heat-resistant thermoplastic resin like PEEK and PEK owing to their similarity in chemical structure, PTK has been studied to some extent to date. There are some disclosure on PTKs, for example, in Japanese Patent Laid-Open No. 58435/1985 (hereinafter abbreviated as "Publication A"), German Offenlegungsschrift 34 05 523A1 (hereinafter abbreviated as "Publication B"), Japanese Patent Laid-Open No. 104126/1985 (hereinafter abbreviated as "Publication C"), Japanese Patent Laid-Open No. 13347/1972 (hereinafter abbreviated as "Publication D"), Indian J. Chem., 21A, 501-502 (May, 1982) (hereinafter abbreviated as "Publication E"), and Japanese Patent Laid-Open No. 221229/1986 (hereinafter abbreviated as "Publication F").
Regarding the PTK described in the above publications, neither molding nor forming has however succeeded to date in accordance with conventional melt processing techniques. Incidentally, the term "conventional melt processing techniques" as used herein means usual melt processing techniques for thermoplastic resins, such as extrusion, injection molding and melt spinning.
The unsuccessful molding or forming of PTK by conventional melt processing techniques is believed to be attributed to the poor melt stability of the prior art PTKs, so that they perhaps tended to lose their crystallinity or to undergo crosslinking and/or carbonization, resulting in a rapid increase in melt viscosity, upon their melt processing.
It was attempted to produce some molded or formed products in Publications A and B. Since the PTKs had poor melt stability, it was only possible to obtain certain limited types of molded or formed products by a special molding or forming process such that a great deal of a fibrous reinforcing material is either impregnated or mixed with PTK as a sort of binder and the resultant mixture was then molded or formed under pressure.
Since the conventional PTKs are all insufficient in melt stability as described above, it has been unable to obtain molded or formed products even from compositions of the PTK with other thermoplastic resins and fillers, to say nothing of the PTK alone, by applying conventional melt processing techniques.